Subcutaneous and intramuscular delivery of liquid drugs by injection is common in the medical arts. As some medications such as insulin must be given frequently by injection to an individual, easy performance of the injections is desirable.
Many patients dislike needle injections due to pain or fear for needles. Further, blood-borne pathogens, such as HIV and hepatitis, can be transmitted to health care workers by accidental needle-sticks. Also, the disposal of used needles is a growing concern. This disposal presents a problem to individuals other than healthcare workers. Children, for example, may find used needles in the garbage, putting them at risk of contracting infection. Discarded needles likewise pose a risk to waste disposal workers. This is at the moment a huge worldwide problem, (though partly overlooked as it mainly hits countries of low development) causing deaths counted in millions,
In efforts to minimize the fears and risks associated with needle injections, several types of needle-free jet injectors have been developed. These devices penetrate the skin using a high velocity fluid jet and deliver medication into the tissue of a patient. In order to accomplish this, a force is exerted on the liquid medication. Jet injectors in general contain a fluid drug which has been transferred into a chamber having a small orifice at one end. A drive means, e.g. a ram, is accelerated using either a coil spring or a compressed gas energy source. The ram impacts a plunger which in turn creates a high pressure impulse within the chamber. This pressure impulse ejects the fluid medicament through the orifice at high velocity, piercing the skin. The energy source continues to apply a force to the plunger which quickly propels the drug through the opening in the skin, emptying the injection chamber in a fraction of a second. The drive means may be adapted to provide a two-stage injection, i.e. a first penetrating burst of drug at a high pressure followed by a subsequent delivery of the remaining amount of drug at a lower pressure. It shall be noted that the same principle of having a pressurized injection device can also be used for needle-injectors, in the case where it is desirable to enable an injection without a person having to press in the drug by her- or him-self when injecting. This can be the case if it is desirable to have a well known injection pressure and time, or if the user feels discomfort by having to perform the actual injection.
The energy impulse exerted on the pressurized injector in order to provide a sufficiently high-powered injection, especially when performing jet injections, is of a magnitude which require an energy source with a power level higher than is known from conventional manual injection devices. Systems that require a higher pressure or a certain level of automation often benefit from a build-in energy source such as a gas cartridge, pyrotechnical unit or a mechanical spring. The main advantage of using a mechanical spring is the ability of re-use whereas the e.g. gas operated systems require exchange of the gas unit or discarding of the whole device when it has been used. However, the pre-stressing of a spring requires a certain level of force provided by the user or some additional power such as a motor which again require either batteries or an external energy supply. To ensure handling simplicity, manual loading by the user is thus desirable.
There are several spring operated injection systems on the market addressing this problem. In most cases the spring is either loaded by a twisting operation or a separate device dedicated for the loading procedure. The devices that require a twisting operation by the user are in many cases (e.g. MHI 500 of the Medical House disclosed in EP 1332767 and Ltd. Medi-Jector Vision of Antares Pharma disclosed in U.S. Pat. No. 5,879,327) designed with a thread for the spring pre-stressing operation. Such a thread will impose a certain degree of mechanical loss depending on the friction of the thread interaction. This causes an unwanted additional effort by the user. Other known devices are described in US 2006089593 and EP 0834330, where only a single set of one-way fixation means are provided.
In view of the above, one of the objectives of the present invention is to provide a mechanism for loading a pressurized injection device which enables the device to be manually loaded.
It is a further objective of the present invention to provide a loading mechanism that ensures the injection device is reusable.
Yet a further objective is to provide a loading mechanism which is effective in extracting maximum gain from the loading force provided by the user through an efficient gearing and low friction.
A further objective is also to ensure ease of handling by the user.
A further objective of the present invention is to provide a simple loading mechanism for a pressurized injection device.
In the alternative, it is a further objective to provide a pressurized injection device with resemblance of a conventional pen type injector as regards function and configuration, in order to make the patient comfortable with the jet injection device and so that the injection device can easily be utilized by a non-professional user, e.g. a insulin requiring diabetic.